The present disclosure relates to subject matter contained in priority Japanese Patent Application No. 2000-015968, filed on Jan. 25, 2000, the contents of which is herein expressly incorporated by reference in its entirety.
1. Technical Field of the Invention
The present invention relates to a method and a device for detecting substrates accommodated and transferred in a sealed container in the manufacture of thin film devices or magnetic heads that constitute semiconductor elements, liquid display panels, solar cells, and the like.
More particularly, the present invention relates to such systems enabling detection of the presence and position of each of a plurality of substrates, to which thin film forming processes are to be performed, within the sealed container. Throughout this disclosure, the term xe2x80x9csubstratexe2x80x9d will be used for purposes of consistency to refer to planar substrates such as silicon wafers and glass flat panes, but it will be understood that it is intended to be used in the broad context so as to be applicable to all substrates.
2. Description of Related Art
Vigorous efforts are being made to enable more precise, accelerated processes for substrates of larger size, for cost effective, high-yielding and profitable manufacturing of thin film devices. While stringent control of particulate contamination is imperative for further miniaturization of thin film devices, it is not desirable that xe2x80x9cclean roomsxe2x80x9d be established with a large, complex design, because the equipment cost will rise accordingly. For that reason, it has been known to employ a sealed container or pod for maintaining substrates such as wafers fairly clean within a substantially particle free environment and for storing and transferring the substrates in a sealed condition from one to another of various processing stations in a substrate transfer system generally referred to as a xe2x80x9cmini-environmentxe2x80x9d. More recently, these containers are of the FOUP (Front Opening Unified Pod) design intended to carry semiconductor wafers sized to a diameter of 300 mm. The substrate transfer system using such FOUP type containers, wherein only the interior of the containers are maintained particle free, is fairly advantageous because it does not require a bulky clean room, while being able to transfer the wafers in a highly clean environment.
The sealed container of the FOUP design has in its interior a desired number of rack members for supporting the wafers generally horizontally, in a generally vertically spaced relationship. When the sealed container is moved to a predetermined position within a film forming apparatus, its front door is opened, and prior to the removal of the substrates therein, sensors inform whether each of the substrates is present, and whether the substrates are properly positioned in their respective rack members. This detection of the presence and position of substrates is conducted for the purpose of accommodating the substrates properly back in their original places and positions after a film forming operation has been performed to the substrates.
The sealed containers of the FOUP design are typically provided as two standard sizes: a smaller size that holds thirteen wafers and a larger size that holds twenty-five wafers. In a processing system, several such FOUP type sealed containers are loaded in a predetermined positional relationship with a film forming apparatus.
With reference to FIG. 4, when the sealed containers 1 are brought in a parallel arrangement with each other at predetermined locations, their front doors (not shown) are horizontally moved toward the film forming apparatus (not shown) side by means of a door removing mechanism (not shown) generally referred to as a xe2x80x9cFOUP front openerxe2x80x9d, whereby the containers 1 are opened to provide access to the interior thereof. A wafer handling robot 4 that faces the sealed containers 1 holds wafers 2 with its blades 3 and transfers them into a film forming station, as well as brings back the processed wafers 2 and stores them in their original places and positions within the container 1. The wafer handling robot 4 is moved along transfer rails 7 and brought to a position facing one of the sealed containers 1 of which front door has just been opened.
The sensing of substrates within the sealed container was conventionally accomplished in such a manner as described below. A reflection sensor 9 is attached on the opposite side of the blade 3 of the wafer handling robot 4, and when the wafer handling robot 4 is positioned in front of the opening of the sealed container 1, the blade 3 is rotated at 180 degrees by operating a plurality of (four in the illustrated example) arms 8 of a link mechanism, so that the reflection sensor 9 faces the opening of the sealed container 1 as shown in the drawing. The wafer handling robot 4 is designed to be capable of positioning the reflection sensor 9 in relation to each of the wafers 2 within the container 1, using the arms 8. The reflection sensor 9 is first positioned so as to face an uppermost wafer 2 in the container 1.
In this state, a detection circuit built in the wafer handling robot 4 activates the reflection sensor 9, and determines the presence of the wafer 2 in its rack member based on the result whether a spot light projected from the reflection sensor has been reflected by the wafer. The wafer handling robot 4 is lowered intermittently in a certain pitch space corresponding to the intervals between the vertically spaced rack members in the container 1, and detects the presence of the wafers 2 in each of the rack members in succession from top to bottom. When the wafer handling robot 4 has completed its detecting operation, it rotates its arms 8 at 180 degrees so that the wafer transfer blade 3 faces the wafers 2, and rises to a position where the wafer transfer blade 3 comes opposite the uppermost wafer 2 in the container 1, after which the wafer 2 is removed from the container and carried toward a processing system.
As described above, according to the conventional substrate detecting method, the wafer handling robot 4, which is intended to be used for inserting and removing substrates to/from the container 1, is doubled as the means for detecting the substrates. There is normally provided only one such wafer handling robot 4 in a processing system, where there are often a plurality of sealed containers 1 located in their respective predetermined positions. Therefore, until after all of the wafers 2 in one container have been inserted or removed to/from the container, detection of wafers 2 in other containers cannot be commenced. Life of the entire substrate handling system is shortened because the wafer handling robot 4 cannot withstand the demanding work for the both purposes of transferring and detecting the substrates. With such substrate transfer system with only one wafer handling robot, when a large number of containers 1 are provided, the transferring efficiency of substrates becomes extremely low, and troubles are more likely to occur. Furthermore, defects may be formed on thin films on the substrates due to dust which is attributable to the rough use of the substrate handling system.
Also, in order to make the wafer handling robot 4 double as the means for detecting substrates in addition to its intended use for transferring substrates, it is necessary to provide a large number of drive shafts and other mechanisms to the robot for enabling complex movements, for which its internal structure becomes complex, the cost high, and the reliability low.
Another problem is that the reflection sensors sometimes make an error especially when the rack members in the container 1 are out of position even slightly because of a dimensional error. For sensing thin substrates such as wafers, reflection sensors of limited reflection type are used, in which a spot light of extremely small diameter is projected from the reflection sensor, so that wafers opposite and spaced from the sensor are detected. Even so, when the wafer is offset in the rack member in either one of forward and backward directions, or when the end surface processing of the wafer has been insufficient, even the reflection sensor of the limited reflection type can often make an error.
In view of the foregoing, it is an object of the present invention to provide a method and a simple mechanism for sensing substrates within a container reliably at high speed without using the substrate transferring system.
To accomplish the above object, the present invention provides a substrate detection device incorporated in a sealed container for storing therein and transferring a plurality of substrates. The sealed container includes a container housing, a removable front door, and a door moving mechanism including a door fixing unit for fixedly holding the front door, and a lifting block operatively connected to the door fixing unit for moving the door fixing unit upward and downward so as to open and close the container housing with the front door. The substrate detection device of the present invention preferably includes: a pair of gear wheels rotatably supported in mutual engagement for synchronous rotation and accommodated within a recess in the door fixing unit at a position near an upper end thereof; a pair of support arms attached to the pair of gear wheels respectively at base ends thereof; a sensor comprising a light-transmitting unit and a light-receiving unit which are respectively mounted at distal ends of the pair of support arms; a cam member rotatably mounted on the door fixing unit and connected to one of the pair of gear wheels such as to transmit rotation thereto; a cam groove formed in the cam member; and a cam follower mounted on a stationary part of the door moving mechanism at a position where it engages with the cam groove when the cam member is lowered integrally with the door fixing unit.
Preferably, the cam groove is configured such that the engagement between the cam follower and the cam groove causes rotation of the gear wheels, whereby the support arms are rotated into the sealed container and located on both sides of an uppermost substrate within the sealed container.
In one preferred embodiment of the present invention, the cam follower is attached on an actuator mounted on the stationary part of the door moving mechanism so that the cam follower is advanced forward to engage with the cam groove and retracted backward to disengage therefrom.
In another preferred embodiment of the present invention, the cam groove comprises a curved first track and a linear second track, the cam follower being engaged with the first track when the cam member is lowered integrally with the door fixing unit, and engaged with the second track when the cam member is lifted integrally with the door fixing unit.
While novel features of the invention are set forth in the preceding, the invention, both as to organization and content, can be further understood and appreciated, along with other objects and features thereof, from the following detailed description and examples when taken in conjunction with the attached drawings.